The impact factor for the virtual photon to light vector meson transition

We evaluate in the next-to-leading approximation the forward impact factor for the virtual photon to light vector meson transition in the case of longitudinal polarization. We find that in the hard kinematic domain, both in the leading and in the next-to-leading approximation, the expression for the impact factor factorizes, up to power suppressed corrections, into the convolution of a perturbatively calculable hard-scattering amplitude and a meson twist-2 distribution amplitude.Comment: 31 pages latex; few comments and one reference added; version to appear in Eur. Phys. Journal

Photon-Reggeon Interaction Vertices in the Nla

We calculate the effective vertices for the quark-antiquark and the quark-antiquark-gluon production in the virtual photon - Reggeized gluon interaction. The last vertex is considered at the Born level; for the first one the one-loop corrections are obtained. These vertices have a number of applications; in particular, they are necessary for calculation of the virtual photon impact factor in the next-to-leading logarithmic approximation.Comment: 20 pages, references adde

Inclusive production of a pair of hadrons separated by a large interval of rapidity in proton collisions

We consider within QCD collinear factorization the inclusive process $p+p\to h_1+h_2+X$, where the pair of identified hadrons, $h_1,h_2$, having large transverse momenta is produced in high-energy proton-proton collisions. In particular, we concentrate on the kinematics where the two identified hadrons in the final state are separated by a large interval of rapidity $\Delta y$. In this case the (calculable) hard part of the reaction receives large higher order corrections $\sim \alpha^n_s \Delta y^n$. We provide a theoretical input for the resummation of such contributions with next-to-leading logarithmic accuracy (NLA) in the BFKL approach. Specifically, we calculate in NLA the vertex (impact-factor) for the inclusive production of the identified hadron. This process has much in common with the widely discussed Mueller-Navelet jets production and can be also used to access the BFKL dynamics at proton colliders. Another application of the obtained identified-hadron vertex could be the NLA BFKL description of inclusive forward hadron production in DIS.Comment: 29 pages, 9 figures; corrected few typos and added an acknowledgment; version to be published on JHEP. arXiv admin note: substantial text overlap with arXiv:1202.108

Infrared safety of impact factors for colourless particle interactions

We demonstrate, to next-to-leading order accuracy, the cancellation of the infrared singularities in the impact factors which arise in the QCD description of high energy processes A + B -> A' + B' of colourless particles. We study the example where A is a virtual photon in detail, but show that the result is true in general.Comment: 31 pages latex including 10 figure

Glueball spectrum and the Pomeron in the Wilson loop approach

Using a nonperturbative method based on asymptotic behaviour of Wilson loops we calculate masses of glueballs and corresponding Regge-trajectories. The only input is string tension fixed by meson Regge slope, while perturbative contributions to spin splittings are defined by standard alpha_s values. The masses of lowest glueball states are in a perfect agreement with lattice results. The leading glueball trajectory which is associated with Pomeron is discussed in details and its mixing with f and f' trajectories is taken into account.Comment: LaTeX2e, 49 pages, 2 figure

Central exclusive production of scalar \chi_c meson at the Tevatron, RHIC and LHC energies

We calculate several differential distributions for exclusive double diffractive $\chi_c(0^{++})$ production in proton-antiproton collisions at the Tevatron and in proton-proton collisions at RHIC and LHC in terms of unintegrated gluon distributions (UGDFs) within the $k_t$-factorisation approach. The uncertainties of the Khoze-Martin-Ryskin approach are discussed in detail. The $g^* g^* \to \chi_c(0^{++})$ transition vertex is calculated as a function of gluon virtualities applying the standard pNRQCD technique. The off-shell effects are discussed and quantified. They lead to a reduction of the cross section by a factor 2--5, depending on the position in the phase space and UGDFs. Different models of UGDFs are used and the results are shown and discussed. The cross section for diffractive component depends strongly on UGDFs. We calculate also the differential distributions for the $\gamma^* \gamma^* \to \chi_c(0^{++})$ fusion mechanism. The integrated cross section for photon-photon fusion is much smaller than that of diffractive origin. The two components have very different dependence on momentum transfers $t_1, t_2$ in the nucleon lines as well as azimuthal-angle correlations between both outgoing nucleons.Comment: 34 pages, 23 figures, 2 table

Radiative Corrections to γγ→ttˉ\gamma\gamma\to t \bar t in the Electroweak Standard Model

The cross-section for $\gamma\gamma\to t \bar t$ with arbitrary polarized photons is calculated within the electroweak Standard Model including the complete virtual and soft-photonic $O(\alpha)$ corrections. We present a detailed numerical discussion of the radiative corrections with particular emphasis on the purely weak corrections. These are usually of the order of 1--10\% for energies up to 1 TeV. For unpolarized or equally polarized photons they reach almost 10\% close to threshold. The large corrections cannot be traced back to a universal origin like the running of $\alpha$ or the $\rho$-parameter. Apart from the energy region around the Higgs resonance $(\gamma\gamma\to H^*\to t\bar t)$ the weak corrections are widely independent of the Higgs-boson mass.Comment: 22 pages, LaTeX (compressed, uuencoded), 20 figures as compressed uuencoded ps-files, complete ps-file available via anonymous ftp from ftp://ftp.physik.uni-wuerzburg.de/pub/preprint/WUE-ITP-95-017.p

The BFKL Pomeron in 2+1 Dimensional QCD

We investigate the high-energy scattering in the spontaneously broken Yang - Mills gauge theory in 2+1 space--time dimensions and present the exact solution of the leading $\ln s$ BFKL equation. The solution is constructed in terms of special functions using the earlier results of two of us (L.N.L. and L.S.). The analytic properties of the $t$-channel partial wave as functions of the angular momentum and momentum transfer have been studied. We find in the angular momentum plane: (i) a Regge pole whose trajectory has an intercept larger than 1 and (ii) a fixed cut with the rightmost singularity located at $j=1$. The massive Yang - Mills theory can be considered as a theoretical model for the (non-perturbative) Pomeron. We study the main structure and property of the solution including the Pomeron trajectory at momentum transfer different from zero. The relation to the results of M. Li and C-I. Tan for the massless case is discussed.Comment: 28 pages LATEX, 3 EPS figures include

Q2-evolution of parton densities at small-x values

In the leading twist approximation of the Wilson operator product expansion with "frozen" and analytic strong coupling constants we show that Bessel-inspired behavior of the structure function F2 at small x, obtained for a flat initial condition in the DGLAP evolution equations, leads to good agreement with the deep inelastic scattering experimental data from HERA.Comment: 19 pages, 5 figures, published in the Proceedings of Workshop on Physics of Fundamental Interactions, Institute of High Energy Physics, Protvino, Russia, 22--25 December 2008 (Phys.Atom.Nucl. in press